1. Field of the Invention
The present invention relates to a monolithically integratable circuit arrangement having at least one inductor, formed as a conductor loop, and at least one capacitor, connected to the conductor loop, and relates to an integrated circuit with a circuit arrangement of this type.
2. Description of the Background Art
Circuit arrangements of this type are used particularly for the processing of high-frequency electromagnetic signals, for example, in the gigahertz range, e.g., in oscillators, mixers, amplifiers, filters, and matching circuits for transmitting/receiving devices of communication systems.
FIG. 5 shows by way of example a circuit diagram of a voltage-controlled oscillator (VCO) with a known circuit arrangement of this type. The differentially realized VCO has a tank circuit with an inductor formed as conductor loop L1 and a tunable capacitor Ct, as well as an amplifier circuit for maintaining (undamping) the oscillation. The amplifier circuit made as an emitter circuit is connected, both on the input side and on the output side, to the conductor loop which to clarify the size relationships is not shown symbolically in FIG. 5b but in the form of its layout. The collector terminals of the transistors of the amplifier circuit are supplied with the necessary DC potential (bias) Vc via a DC terminal in the middle of the conductor loop, whereas the DC potential Vb is supplied to the base terminals via (bias) resistors Rb. Capacitors Cd are provided to block off DC compensating currents.
The inductor (“coil”) is therefore used simultaneously in the high-frequency range (as part of the tank circuit) and utilized as the DC feed. As a coupling element, it is connected between the inputs and outputs of the amplifier transistors, so that blocking capacitors Cd are necessary because of its DC conductivity.
It is a disadvantage here that the arrangement of the elements in the area of both ends of the conductor loop is problematic. The capacitive elements Ct, Cd require a relatively large (chip) area, so that long supply lines are needed in part, which causes an increase in parasitic effects, or else the surface area of the capacitive elements must be limited, which has a disadvantageous effect on the efficiency of the VCO circuit (limited frequency tunability, rather high phase noise, etc.).
Another disadvantage is that even minor differences in the resistance values of the two bias resistors Rb, e.g., due to technology or process variations, lead to different potentials at the bases of the transistors and thereby to different collector currents. This has the result of an asymmetric operation (offset), which disadvantageously results in increased noise and a lower output power.
It is disadvantageous in addition that the blocking capacitors Cd narrow the usable frequency tuning range and as a result of parasitic capacitors worsen the entire electrical behavior of the circuit.